1. Field of the Invention
The present invention relates generally to disk drives, and particularly to a suspension-level piezoelectric microactuator for read/write heads for disk drives.
2. Description of Related Art
One of the main avenues for the increase in storage capacity of disk drives is through reduction of the track pitch of the recorded information. The minimum distance between recorded data tracks is limited by the ability of a voice coil motor (VCM)xe2x80x94actuated servo system to accurately maintain the position of the recording heads over a given track.
The positioning capability of this servo system is limited by its bandwidth, which in turn is constrained by the power available to the VCM and by suspension resonances. The resolution of the actuator""s motion is also limited by stiction in the pivot""s ball-bearings. Both of these constraints are approaching fundamental limits after which further increase in track density will be not be possible with the current technology.
To improve track density, proposals have been made to implement second-stage, fine-positioning, in addition to first-stage, coarse positioning. For example, Takaishi et al. propose a secondary microactuator which is built into the head assembly structure, as part of the head mounting block, between the head suspension and the head assembly arm (xe2x80x9cMicroactuator Control For Disk Drivexe2x80x9d, Takaishi et al., IEEE Transactions on Magnetics, Vol. 32, No. 3, May 1996). Another secondary actuator arrangement is described in U.S. Pat. No. 5,521,778 to Boutaghou et al., wherein the secondary actuator 30 connects one end of a further arm portion (a load beam 25) to an actuator arm 24 and wherein a slider 26 and head are supported at the opposite end of the load beam 25.
In each of the above-referenced proposed systems, a substantial length of the head support structure is located between the head and the secondary actuator. For example, as shown in FIG. 4 of the Takaishi et al. article, a head suspension, which accounts for a significant portion of the length of the structure supporting the head, extends from the secondary actuator to the head. Similarly, as shown in FIG. 1 of the Boutaghou et al. patent, the load beam 25, which accounts for about one-half of the length of the structure supporting the head, extends from the secondary actuator to the head.
As such, each of these structures may be susceptible to a significant level of structural resonance, upon operation of the secondary actuator. Such resonance tends to result in unwanted head motion, which inherently reduces the accuracy of the positioning operation and, thus, reduces the available track density.
Accordingly, there is a need in the art for a microactuator for supporting and finely-positioning a read and/or write head with sufficient accuracy to operate with a track pitch substantially below that possible with typical VCM servo system operation.
To address the requirements described above, the present invention discloses a suspension-level piezoelectric microactuator for the fine positioning of a head-arm assembly of a disk drive. The microactuator is manufactured from a generally flat metal sheet structure having a central beam and two tabs extending from opposite sides of the beam. At least one layer of piezoelectric material is bonded onto each of the two tabs. Each of the two tabs is bent, with the piezoelectric layers bonded thereto, to a position substantially normal to the central beam. The structure is then joined to the distal end of a suspension member of the head-arm assembly. A recording head is connected to the central beam of the microactuator. When a voltage is applied to the piezoelectric materials, deflection of the microactuator occurs, thereby positioning the recording head.
It is an object of the present invention to employ a second-stage, fine-positioning piezoelectric microactuator for positioning one or more heads of a disk drive relative to a recording surface. It is yet another object of the present invention to provide such a piezoelectric microactuator as a relatively small, light-weight device, located between the head and the suspension member of the head-arm assembly to exclude suspension resonance. It is a further object of the present invention to provide such a piezoelectric microactuator that is capable of very small movements on the order of at least one half the track width, for example, on the order of about 0.5 xcexcm for a track pitch of about 1.0 xcexcm. It is yet a further object of the present invention to provide such a piezoelectric microactuator that is capable of nanometer scale movements.